Electromotor

ABSTRACT

A stator is mounted in a housing of an electromotor, and a rotor is journalled for rotation in the housing relative to the stator. Impeller means rotates with the rotor and inherently tends to create audible sound frequencies in response to rotation in the ambient atmosphere. A requisite number of commuting or spoiler portions are provided on the impeller means such that upon rotation of the latter, substantially 15000 such spoiler portions pass per second any fixed point of the housing with reference to which the impeller turns. This commutes the audible sound frequencies to inaudible sound frequencies, that is sound frequencies which are normally inaudible to the human ear so that the electromotor is quieter to a listener.

United States Patent 1 1 Schnitzler, Jr.

154] ELECTROMOTOR [75] Albrecht Schnitzler, Jr., Nurtlingen/Wurtt, Germany Metabowerke KG Closs, Rauch & Schnizler, Nurtingen/Wurttemberg, Germany 22 Filed: Aug. 26, 1970 21 App1.No.: 67,151

lnventor:

[73] Assignee:

[30] Foreign Application Priority Data Aug. 27, 1969 Germany ..P 19 43 478.7

[56] References Cited UNITED STATES PATENTS 3,476,960 11/1969 Rees ..310 50 3,121,220 2/1964 Buckwa1ter.. ...1 16/147 x 2,528,026 10 1950 Allen et a1 ..116/147 x 2,881,337 4/1959 Wall ..310/51 X 1 Mar. 27, 1973 Primary ExaminerRichard B. Wilkinson Assistant ExaminerU. Weldon AttorneyMichael S. Striker [57] ABSTRACT A stator is mounted in a housing of an electromotor, and a rotor is journalled for rotation in the housing relative to the stator. Impeller means rotates with the rotor and inherently tends to create audible sound frequencies in response to rotation in the ambient atmosphere. A requisite number of commuting or spoiler portions are provided on the impeller means such that upon rotation of the latter, substantially 15000 such spoiler portions pass per second any fixed point of the housing with reference to which the impeller turns. This commutes the audible sound frequencies to inaudible sound frequencies, that is sound frequencies which are normally inaudible to the human ear so that the electromotor is quieter to a listener.

5 Claims, 3 Drawing Figures PATFNTEUMARPJ m5 INVENTOR Austen! 5600/2651 BY 4 /411 //fl.

ATTORNEY ELECTROMOTOR BACKGROUND OF THE INVENTION The present invention relates generally to electromotors, and more particularly to fast electromotors.

Such electromotors are of course already known. They are used, among other applications, for driving electrically operated tools, for powering various household appliances and devices, and in other similar applications. They utilize an impeller provided with blades which rotatesin the ambient atmosphere and which, considering that these electromotors-which are frequently universal motorsrotate at high speed, produces substantial and objectionable noise, especially at the high idling speed of such'motors. In fact, this noise frequently is more objectionable even than noises which are originated in the journalling or for instance by the gearing associated with the motor.

These noises can be particularly objectionable where quietness is normally desired, for instance in certain household appliances, or where medical considerationsfor instance possible damage to hearing-play a role as in the use of such motors in tools.

SUMMARY OF THE INVENTION It is accordingly an object of the present invention to avoid the aforementioned disadvantages.

More particularly, it is an object of the present invention to provide a fast-rotating electromotor which avoids these disadvantages.

. Still more specifically it is an object of the invention to provide such an electromotor the noises from whose impeller are substantially reduced or even entirely eliminated, and in which no other supplementary steps are necessary to suppress or reduce noise.

In pursuance of the above objects, and others which will become apparent hereafter, resides, briefly stated, in an electromotorwhich comprises a housing, stator means in the housing, and rotor means journalled for rotation in the housing relative to the stator means. lmpeller means is rotatable with the rotor means and inherently tends to create audible sound frequencies'in response to rotation in the ambient atmosphere. According to the invention commuting means is provided for commuting such audible sound frequencies into inaudible sound frequencies during rotation of the impeller means. The term commuting the audible sound frequencies to inaudible sound frequencies signifies that the sound frequencies which are produced by an impeller of a motor constructed according to the present invention, are outside and above the normal hearing frequency of a human being, so that the noises still produced by the impeller means cannot be heard by the human ear. In fact, and particularly during idle operation of an electromotor constructed in accordance with the present invention, the sound frequencies produced are in the ultrasonic frequency range and thus no longer objectionable.

The purposes of the present invention are accomplished in that the commuting means is provided in form of a plurality of commuting portions or spoiler portions provided on the impeller means, and the number of spoiler portions includes any and all blades which may be provided on the impeller means in accordance with conventional practice. The number of such spoiler portions provided is so selected that at the operating speed of rotation of the impeller means substantially 15,000 spoiler portions per second pass a fixed point of the housing. In other words, the number of rotations per second multiplied by the number of spoiler portions provided on the impeller means should result in a total of 15,000 or more. If, for instance, the impeller means has an outer diameter of at most mm, then it should have a minimum of 35 spoiler portions which, as also conceived by the invention, will pass with small spacing past the air-outlet apertures or passages provided in the housing for the purpose of permitting the escape of air displaced by the impeller means.

It should be pointed out that in place of or in addition to the blades of the impeller means itself, the spoiler portions may also be in form of pins or other projections provided on and distributed about the circumference of the impeller means, although it is clear that configurating all of the spoiler portions in form of blades of the impeller means will be the most advantageous arrangement. It must be pointed out in this connection that in many instances the number of blades thus provided will be substantially higher than the number of blades actually required for the proper functioning of the impeller means, and that this excess number of blades can result in a certain loss of effectiveness of the impeller means. However, this is acceptable especially in electromotors used for electrically operated tools, because the undesired running away of the motor is avoided or is made less likely thereby.

In any case, by resorting to the present invention the objectionable audible sound frequencies are commuted to and raised to inaudible sound frequencies, that is to a frequency level which is no longer audible to the human ear. If for instance the impeller means rotates at a speed of substantially 20,000 rpm, then a minimum of 45 of the inventive spoiler portions will be provided on its circumference, circumferentially distributed thereabout.

According to the invention it is also advantageous although not necessary that the impeller means itself be constructed in known and conventional manner as a radial-flow impeller and the air outlet openings in the housing are constituted by slots or slits provided in the housing.

By contrast to known constructions the diameter of the impeller means can be selected so large that the ends or outer edges of the impeller blades pass the slots in the housing with very small spacing, that is the diameter of the impeller means can be almost equal to-except for a gap of a few millimeters-the inner diameter of the housing which is determined by the dimensions of the field packet, that is the package of lamellae about which the field winding is placed.

The guidance of air for cooling of the motor is substantially improved if the blades of the impeller means are covered at their axial end in the radially outer area and that this isaccomplished by providing a housing wall portion extending transversely to the axis of rotation of the impeller means and provided with a cut-out concentric to this axis of rotation and having a diameter which approximately corresponds to the diameter of the rotor package, that is the package of lamellae about which the rotor winding is convoluted.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims.

The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic axial section through an electromotor according to the present invention;

FIG. 2 is a fragmentary detail view,-on an enlarged scale, showing the area circled in chain lines in FIG. 1 and identified with numeral II; and

FIG. 3 is a section taken on line lll-lll of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail it will be seen that the illustrated electromotor is auniversal motor. It is provided with a housing 1 accommodating a field packet 2 of a stator, that is a package of lamellae about which the field winding 3 is convoluted. In turn it surrounds an anchor package 4, that is the package of lamellae associated with the rotor and surrounded by the anchor or armature winding 5. Packet 4 is penetrated by the rotatable shaft 6, being separated from the same by an insulating sleeve 7.

An impeller wheel 8 is mounted on the shaft 6 or on the sleeve 7 and as the drawing clearly shows it has an outer diameter which is just slightly smaller than the inner diameter 9 of the housing 1, which inner diameter is determined by the dimensions of the field packet 2. The housing 1 is provided in the general plane of the impeller wheel 8 with a plurality of air outlet channels 11 which are configurated as slits 10 in the housing wall, and in the illustrated embodiment there are four of these channels 11 provided distributed circumferentially about the housing, as is shown in FIG. 2.

According to the present invention the impeller wheel 8 is provided with a large number of spoiler portions, which here are in form of blades 12 which extend radially and which have an air incidence angle 13 of approximately 40".

lnthe illustrated embodiment the number of blades 12 corresponds to the number of spoiler portions 14 which are defined by the outer edges of the blades 12, because it is the blades 12 themselves which constituteor rather whose outer edge constitute-the spoiler portions 14. These outer edges pass very closely Despite the high number of such blades a completely adequate passage. of air is obtained, and the cooling effect is advantageously influenced in that the blades 12 are provided or rather covered at one axial end in the radially outer region by a housing wall 16 which extends transversely of the axis of rotation and is provided with a cut-out l7 concentric with the axis of rotation and having a diameter which corresponds approximately to the outer diameter of the anchor packet 4 of lamellae.

It will be appreciated that modifications are possible and will indeed offer themselves to those skilled in the art, and that such modifications can be made without departing from the scope and concept of the invention as set forthherein and expressed in the appended claims. It will also be appreciated that the advantages obtained with the present invention are primarily to be found in the fact that the heretofore so objectionable audible noises produced by the impeller wheel 8 rotating at high speed are either completely eliminated or almost completely eliminated and will in no case be objectionable any longer. It thus appears tothe listener as if the motor were in fact running quietly.

Resort to the present invention does not materially increase the expenses involved in producing the electromotor, particularly if the impeller wheel 8 is made of synthetic plastic material, in which case the large number of spoiler portions--here the substantially larger number of blades 12-does not result in any substantial increases in material expense. By resorting to the present invention there is thus produced an electromotor which is very quiet as far as the audible range of noise is concerned, and which is produced without any special expensive measures and without in fact any appreciable increase in the expense involved heretofore in manufacturing like electromotors but without the present invention incorporated therein.

It will be understood that each of the elements described above, or two or more together, mayalso find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in an electromotor, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. In a motor-driven tool, a combination comprising a housing; an electromotor provided in said housing and comprising a stator, a rotor journalled for rotation to said'stator, and an impeller mounted for rotation and having a plurality of blades so arranged as to supply a flow of cooling air to said electromotor when said impeller rotates and tending to produce audible sound frequencies during such rotation of said impeller; and computing means rotatable with said impeller for commuting said audible sound frequencies to inaudible sound frequencies during rotation of said impeller, whereby said impeller and commuting means, together, comprise a number of interference portions so selected that at normal operating speed of said electromotor at least 15,000 such interference portions per second pass any fixed point of said housing located on a line surrounding the circumference of said impeller and commuting means.

2. In an electromotor as defined in claim 1, said impeller and commuting means having an outer diameter of at most 150 mm, and comprising at least 35 interference portions.

3. In an electromotor as defined in claim 1, all of said interference portions being configurated as impeller blades.

rotation adjacent to said free edges and being provided with a center cutout concentric to said axis of rotation and having a diameter at least substantially approximating said transverse dimension. 

1. In a motor-driven tool, a combination comprising a housing; an electromotor provided in said housing and comprising a stator, a rotor journalled for rotation to said stator, and an impeller mounted for rotation and having a plurality of blades so arranged as to supply a flow of cooling air to said electromotor when said impeller rotates and tending to produce audible sound frequencies during such rotation of said impeller; and computing means rotatable with said impeller for commuting said audible sound frequencies to inaudible sound frequencies during rotation of said impeller, whereby said impeller and commuting means, together, comprise a number of interference portions so selected that at normal operating speed of said electromotor at least 15,000 such interference portions per second pass any fixed point of said housing located on a line surrounding the circumference of said impeller and commuting means.
 2. In an electromotor as defined in claim 1, said impeller and commuting means having an outer diameter of at most 150 mm, and comprising at least 35 interference portions.
 3. In an electromotor as defined in claim 1, all of said interference portions being configurated as impeller blades.
 4. In an electromotor as defined in claim 1, wherein at least said impeller and commuting means consist at least predominantly of synthetic plastic material.
 5. In an electromotor as defined in claim 3, said blades having free edges facing axially of the axis of rotation of said impeller and commuting means, and wherein said rotor comprises an armature package of predetermined transverse dimension; said housing having a wall portion extending transversely to said axis of rotation adjacent to said free edges and being provided with a center cutout concentric to said axis of rotation and having a diameter at least substantially approximating said transverse dimension. 